The present invention relates to braking systems for large vehicles (e.g., trucks and buses). It finds particular application with antilock braking systems and automatic traction control systems used in conjunction with air-braked systems and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other like applications.
It has become common for vehicles (e.g., commercial air-braked vehicles) to include an antilock braking system (ABS) and automatic traction control (ATC). These vehicles typically include wheel speed sensors, which generate signals for activating the ATC. It has been noticed, however, that under certain conditions, false sensor signals may cause the ATC to activate while the vehicle is parked. Activation of the ATC can override the park brake via anti-compounding plumbing or circuitry. Anti-compounding is a feature of air brake systems which avoids applying the spring actuated park brake and the air actuated service brakes at the same time. More specifically, activation of the ATC may, in turn, cause the park brake to be released, which may cause the vehicle to move (e.g., roll) unexpectedly. Such an event is undesirable if the vehicle is intended to be parked.
False sensor signals, which activate the ATC, may be caused from a variety of sources. For example, since wheel speed sensors are typically mounted on or near the vehicle wheels, vibrations transmitted through the tires are also transmitted to the wheels and, furthermore, to the wheel speed sensors. In this case, the wheel speed sensor may interpret the false signals as wheel movement. More specifically, the false signals may mimic those signals produced by the wheel when the vehicle is moving (and the wheel is rotating).
If an ATC control unit receives a signal from a wheel speed sensor that a drive wheel is moving and determines that the vehicle is stationary, the ATC control unit may determine that the wheel is slipping on, for example, ice. Therefore, the ATC control unit may activate an ATC process to compensate for the “slipping” wheel. More specifically, the ATC process may begin controlling the brake associated with the slipping wheel. Consequently, the ATC processor may cause the vehicle park brakes to be released via typical anti-compounding.
In one prior art system, a park brake status is communicated over a CAN-bus (e.g., J1939) to the ATC control unit for disabling the ATC. One drawback to this system is that it requires a CAN-bus and a processing unit including software for interpreting the park brake status signal communicated over the CAN-bus. Furthermore, such a system requires a communications link between the processing unit and the ATC control unit for disabling/enabling the ATC. The processing unit and software for interpreting the park brake status signal are not available on all vehicles.
The present invention provides a new and improved apparatus and method which addresses the above-referenced problems.